Method and apparatus for making plastic articles

ABSTRACT

A method and apparatus for molding an end portion of a tubular thermoplastic parison prior to a blow molding operation to form a parision finish and an annular support flange. The method includes closing a laterally movable, sectional mold onto a circumferential section of a parison so that at least one end portion of the parison extends out of the mold. The extending end portion of the parison is then thermally conditioned to a deformable temperature and thereafter the parison is axially displaced to telescopically insert the thermally conditioned end portion within the mold into general radial alignment with annular, longitudinally spaced finish and support flange cavities. Next, an internal support is telescopically inserted within the thermally conditioned parison portion in preparation for the compression molding steps; which include axially displacing the opposed ends of the parison to force thermally conditioned, deformable plastic parison material radially outwardly into the flange and finish cavities.

This is a Division of application Ser. No. 677,095 filed Apr. 15, 1976now U.S. Pat. No. 4,097,570.

BACKGROUND OF THE INVENTION

This invention relates generally to a method and apparatus forcompression forming both a support flange and a finish on athermoplastic parison. More specifically, the method relates tosequentially compressing the opposed ends of the parison while supportedwithin a forming mold to sequentially form the finish and then thesupport flange.

Over the past several years it has become possible and commerciallydesirable to form blown plastic bottles of reduced wall thickness due toincreased material costs and due to the advent of molecularly orientingthe plastic materials. However, in some cases bottles formed of thisgreatly reduced wall thickness do not have a stacking strength that iscomparable either to the previous, thicker bottles or to glass bottles.This has posed various problems, such as in filling and cappingoperations when the axial strength of the bottle is critical to preventcollapsing.

In an attempt to overcome these specific problems, bottles have beenmade with an annular neck support ledge which is grasped by variousconveying and supporting devices so that the bottle can be pendentlysupported during filling and capping to take the axial load off thebottle during these operations. In fact, this particular arrangement hassolved the collapsing problem. However, because of various problemsencountered, the molding art has not heretofore provided a method andapparatus for forming both the bottle finish and the support flange in asingle operation. One problem is a resistance of certain plasticmaterials to flow into both the finish forming cavity and the flangeforming cavity in a single operation, thus leaving an incompletelyformed bottle. This problem is accentuated with certain plasticmaterials, such as polyethylene terephthalate which crystallizes atelevated temperatures and thus cannot be heated to improve theflowability of the plastic during the compression molding operations.

SUMMARY OF THE INVENTION

The present invention overcomes these and other problems in the art by amethod and apparatus that enable the sequential formation of a finishand a neck support ledge on a parison in a single molding operation.

In one of its broader aspects, the method of this invention includespositioning a thermally conditioned deformable parison portion in a moldin substantial radial alignment with annular, longitudinally spacedfinish and support ring cavities. Next, one longitudinal end of aparison is supported while the other end is axially compressed to forceat least a portion of the thermally conditioned, deformable plasticparison material into at least one of the annular, longitudinally spacedcavities. Then, the previously compressed end of the parison issupported while the previously supported end is compressed to forceadditional thermally conditioned plastic material into at least theother of the annular, longitudinally spaced cavities to complete theformation of the integral finish and support ring on the parison.

In a more limited aspect, the invention includes the steps of firstpositioning an essentially tubular plastic parison in a forming mold sothat at least a portion of the parison projects out of the mold. Theprojecting portion is then placed in heat exchange relationship to athermal conditioning source, such as a radiant heater, to adjust thetemperature of the plastic material in the projecting parison portion towithin a range capable of maintaining the essentially tubularconfiguration yet enabling deformation under compressive forces.

After the projecting portion of the tubular parison has been properlythermally conditioned, that portion is telescopically inserted intogenerally radial alignment with finish and support ring cavities in themold in preparation for the compressive molding steps. The telescopicinsertion is accomplished in the most preferred embodiment by a springbiased push rod which is a part of an axially movable compressivemandrel, the push rod being telescopically inserted freely into thetubular parison to engage the inner surface of a lower, closed,nondeformable, parison end portion. Further downward displacement of thepush rod correspondingly displaces the parison (a) to place the externalsurface of the parison closed end against an axially movable endabutment and (b) to position the thermally conditioned parison portionin general radial alignment with the finish and support ring cavity.

Next, an internal support cylinder on the compression mandrel istelescopically inserted into the thermally conditioned portion of theparison to prevent internal collapse of the parison during thecompression molding steps.

Next, an annular compression ledge on the compression mandrel engagesthe upper end of the parison and longitudinally compresses that endportion to force a portion of the thermally conditioned parison materialinto at least the finish cavity of the mold. During this firstcompression step, the axially movable end abutment is maintained a fixedposition to provide support for the closed end of the parison.

Finally, the end abutment is axially displaced toward the mandrel toforce deformable plastic material radially outwardly into at least thesupport ring cavity to complete the molding operation. Thereafter, thethus-formed parison is removed from the forming mold for additional,optional thermal conditioning in preparation for a subsequent blowmolding operation.

This method and apparatus, therefore, solve a previously existingproblem in the art, namely the inability to completely and properly forma finish and a neck supporting ledge on a plastic article. Thiscapability of the present invention, along with other meritoriousfeatures and advantages, will become more apparent from the followingdetailed description of the invention and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan, schematic view illustrating a rotable turrethaving four radially arranged molds in four different stations in thefinish and neck flange forming operation.

FIG. 2 is a vertical sectional view taken along plane 2--2 as indicatedin FIG. 1, to illustrate a finish forming mold closed upon a parison andpositioned at the thermal conditioning station.

FIG. 3 is a vertical sectional view taken along plane 3--3 as indicatedin FIG. 1, to illustrate the thermally conditioned parison as positionedat the compression molding station.

FIGS. 4-6 are similar to FIG. 3, but illustrate various sequentialphases of the compression molding operation.

FIG. 7 is vertical elevational view of a parison with the integralcompression molded finish and neck support ledge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more specifically to the drawings, the primary object ofthis invention is to form a finish 12 and a neck support ledge or ring14 on a tubular thermoplstic parison 10 as illustrated in FIG. 7, thesupport ledge 14 being utilized in article handling operations to takevertical loads.

According to the invention, these parison components are formedpreferably before a blow molding step by a molding apparatus shown inexemplary form in FIG. 1 and including sectional book type molds20,22,24, and 26 that are pivotally secured to the end portions ofrespective radial arms 28,30,32, and 34 of a rotatable turret 36. Withthis arrangement, the molds are sequentially placed at a loading stationI, a thermal conditioning station II, a compression molding station III,and an unloading or ejection station IV. As indicated, the rotatableturret 36 is rotated in a counter-clockwise manner by a suitable,conventional power means (not shown).

The individual molds, per se, are identical and therefore may beunderstood by reference to FIG. 2, where mold 22 is illustrated at thethermal conditioning station II. Each of the molds include a pair ofsemicylindrical forming molds A, which collectively define annular,longitudinally spaced finish and support ledge cavities, as indicated byletters B and C, respectively. The finish cavity is shown as forming athreaded finish, but may optionally have a configuration to form a lipfinish as is known in the art. Additionally, each mold section includessemi-cylindrical upper and lower support members, D and E respectively,which collectively define annular support rings to assist in graspingand stabilizing the parison during the compression molding operations.

Referring back to FIG. 1, the molding cycle is initiated by firstpositioning a parison, as indicated by reference numeral 38, between theopened sections of a mold at the loading station I. The parisons may beformed by conventional free-extrusion or injection molding techniques.As shown in FIG. 2, the parison is grasped at an intermediate portion sothat at least a portion of the parison projects above the molds forsubsequent thermal conditioning. Of course, the length of the projectingportion should be at least equal to approximately the axial length ofmold segments A and D, as will become apparent in relationship to laterdiscussions of the compression molding steps. Thereafter, the openedsections of the forming mold are closed by means (not shown) and theturret is rotated in a counter-clockwise manner to sequentially positionthe parison at subsequent stations.

Turning now more specifically to FIG. 2, mold 22 is illustrated at thethermal conditioning station II, where the upper, projecting portion ofthe parison 40 is thermally conditioned to a deformable temperature. Thedwell time at the thermal conditioning station will vary based upon theheat absorption characteristics of the particular material, the heatoutput of the heating element at the conditioning station, and thetemperature that must be reached so that the plastic material isdeformable. As an example, polyethylene terephthalate should be heatedto within a range from about 90° C to about 115° C so that the materialis sufficiently deformable during the compression molding step, yet isstill below its crystallization temperature.

In the disclosed embodiment, the thermal conditioning means is in theform of a vertically displaceable heater 42, including an annular heatsource 44 suitably secured within a channel 46 of an annular support 48.The heating element 44 is preferably a radiant, infra-red heat sourcethat is capable of heating the projecting end portion of the parison toa substantially uniform temperature throughout the parison wallthickness.

The heater 42 is vertically movable by suitable conventional means (notshown) to position the heater in two primary locations. The firstlocation is as shown in FIG. 2 to locally heat the projectingcircumferential section of the parison at Station II. The secondlocation for the heater is above the position as shown in FIG. 2 so thatthe turret 36 may be indexed to sequentially position the radiallyarranged molds at the various forming stations.

After sufficiently and properly thermally conditioning the projectingend portion of the parisons at Station II, the heater 42 is displacedvertically upwardly and the thermally conditioned parison is displacedto Station III, where mold 24 is illustrated in FIGS. 1 and 3-6 in axialalignment with a compression molding assembly. That assembly iscomprised of an axially movable compression mandrel 50 and an axiallymovable end abutment 80, both members 50 and 80 being axially movable byappropriate conventional means (not shown).

The compression mandrel 50 is comprised of a head 52 which is suitablysecured to an axially movable displacement rod 54, each of these membershaving a recess 56 and 58, respectively, that collectively form aninternal cavity for a purpose which will become apparent hereinafter.The head member 52 also includes an integral, essentially cylindricalinternal support nose 60 that is inserted within the heated parisonportion for internal support during the compression molding operations.Circumscribing the upper extremity of the support nose 60 is an annularcompression ledge 62 which engages and compresses the upper annular openend of the parison. A secondary ledge 64 is vertically spaced from ledge62 for abutment against the top of the upper support member D when thecompression mandrel is at its lowermost position, as illustrated inFIGS. 5 and 6.

A through-bore 66 extends from recess 56 in head 52 downwardly throughthe center of internal support 60 to receive a push-rod 68 which isemployed to axially displace the parison relative to the forming molds.An enlarged head 70 on the upper end of push-rod 68 limits the axialmovement of the push-rod relative to the compression mandrel as willbecome apparent below. Additionally, a compression spring 74 isinterposed between the lower end of internal support 60 and a bushing 72that is suitably secured on an intermediate portion of the push-rod, thecompression spring serving to downwardly bias the push-rod during theaxial displacement of the parison relative to the forming mold.

The end abutment 80 includes a conical recess 82 to receive the domed,closed-end of the parison.

The steps of operation at the compression molding Station III are asfollows. First, a forming mold, such as 24, is indexed by the rotatableturret into axial alignment with both the compression mandrel 50 and theend abutment 80, the compression mandrel 50, of course, being positionedwell above that position shown in FIG. 3 to accommodate the lateralcircumferential indexing movement of the forming molds and the turret.

Next, the compression mandrel 50 is displaced vertically downwardly tofirst telescopically insert the thermally conditioned parison sectioninto general radial alignment with the finish and neck flange cavitiesand then to compression mold at least a portion of the thermallyconditioned parison material into the finish cavity. This will beunderstood more readily by reference to FIGS. 3, 4, and 5.

FIG. 3 illustrates the compression mandrel just as the lower end of thepush-rod 68 engages the internal surface of the nondeformable, closedparison end. Additionally, it can be seen that the vertical dimension ofthe compression mandrel 50 is such that a longitudinal portion of theinternal support nose 60 has been inserted into the upper, thermallyconditioned parison end. Continued downward movement of the compressionmandrel correspondingly displaces the parison downwardly until theexternal surface of the parison closed end bottoms against the conicalrecess 82 of end abutment 80. Continued downward movement thereafterresults in displacing the internal support 60 fully into the opened endof the parison to the position illustrated in FIG. 4. During this latterphase of downward movement, the push-rod 68 is stationary and theremaining components of the compression mandrel therefore move relativeto the push-rod under the compressive biasing force of compressionspring 74.

FIG. 4 illustrates the compression mandrel at the moment when (a) thethermally conditioned upper end portion of the parison has beengenerally radially aligned with the longitudinally spaced finish andneck support ring cavities, (b) the internal support nose 60 has beenfully inserted into the upper, thermally conditioned section of theparison, and (c) the annular compression ledge 62 has first engaged theupper annular end of the parison. Further downward movement of thecompression mandrel from the position illustrated in FIG. 4 displacesthe extreme upper end of the parison downwardly and results in at leastsome degree of compression molding to force deformable plastic parisonmaterial radially outwardly into at least the finish cavity B.

FIG. 5 illustrates the compression mandrel 50 in its lowermost positionwhere ledge surface 64 engages the top surface of upper support D. Alsoas shown in this Figure, plastic material has been forced radiallyoutwardly to substantially fill the finish cavity due to surface 62compressing the upper extremity of the parison downwardly into theforming mold. During the downward movement of the compression mandrel 50from the position of FIG. 4 to the position of FIG. 5, end abutment 80is maintained in a fixed position to prevent downward movement of theparison during the first phase of compression molding.

When the compression mandrel reaches the position of FIG. 5, upwardmovement of the end abutment 80 is initiated, for example by a suitablypositioned limit switch (not shown) that is tripped by mandrel 50. Theend abutment is upwardly displaced to the position illustrated in FIG. 6to complete the compression molding by forcing formable plastic materialgenerally radially outwardly to fill the neck support cavity C, thuscompleting the compression molding operation. Also as shown by FIG. 6,the compression mandrel is not moved during the upward movement of endabutment 80 in order to provide support to the upper end portion of theparison during the second compression molding step.

Thereafter, the compression mandrel 50 is raised to retract push rod 68to a clearance position above the forming mold. Simultaneously, the endabutment 80 is lowered to the position shown in FIG. 3. Next, the turretmay be rotated to index the compression molded parison to unloadingstation IV, where the mold sections are opened and the parison isejected for placement within a hopper or on a conveyor prior to beingblow molded.

It is to be understood that the disclosed embodiment is merely exemplaryof the overall invention, which is limited only by the following claims.For example, the invention has been explained in reference to a parisonhaving one closed end. For other types of parisons, an alternativevertical displacement component other than the push rod may be required.Additionally, the operation of the compression mandrel and the endabutment were described in terms of a sequential operation. This isdesired only to completely position the thermally conditionedcircumferential section of the parison fully within the forming moldprior to compression by the compression mandrel 50. However, this isoptional and the two compression steps by the compression mandrel 50 andthe end abutment 80 may be simultaneous; for example, the twocompression steps may be carried out simultaneously after the uppermostannular end portion of the parison is inserted within mold portion D.Further, the molds have been described in connection with a rotatableturret, but any other suitable arrangement may be utilized.

Having fully and completely described our invention, we now claim:
 1. Amolding apparatus for forming a finish and an adjacent support flange onan open end of a plastic tube, comprising:a sectional forming molddefining means for receiving a plastic tube including a circularlongitudinal opening, said opening including an annular support flangecavity longitudinally spaced from an annular finish cavity; a verticallymovable compression mandrel axially alignable with the opening in saidforming mold, said mandrel including(a) an essentially cylindricalprojection telescopically insertable within a plastic tube in the moldand radially alignable with the cavities in said mold to internallysupport the tube and (b) an annular ledge circumscribing the upper endof said projection for engaging and axially compressing one end of thetube to force plastic material radially outwardly into at least one ofsaid annular mold cavities; abutment means for engaging and supportingthe other end of said tube including a vertical movable end abutment ina vertical alignment with said compression mandrel; and means foraxially compressing said other tube end to force plastic materialradially outwardly into the other of said annular mold cavities.
 2. Anapparatus as defined in claim 1 wherein said compression mandrel furtherincludes means for engaging the internal surface of a closed end on theplastic tubes to telescopically insert plastic tubes into the formingmold including a spring-biased push rod extending downwardly from saidcylindrical projection.
 3. An apparatus for compression molding aplastic tubular parison to form a finish and an adjacent support flange,an open end of the parison comprising:a laterally displaceable,sectional forming mold and means for closing the forming mold upon anintermediate portion of a tubular parison so that one end portion of theparison projects out of the mold; means for thermally conditioning to adeformable temperature that portion of the parison that projects out ofthe mold; means for axially displacing the parison relative to theforming mold to telescopically insert the thermally conditioned parisonportion into the mold in radial alignment with annular, longitudinallyspaced finish and flange forming cavities in the mold; internal supportmeans telescopically insertable into the thermally conditioned parisonportion for supporting the thermally conditioned portion of the parisonagainst inward radial collapse during the subsequent molding operation;and first and second axially displaceable means for engaging and axiallycompressing the opposed longitudinal ends of the tubular parison toforce thermally conditioned, deformable plastic material radiallyoutwardly into the annular mold cavities.